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    Re: Star photo plate solver
    From: Matus Tejiscak
    Date: 2024 Jun 22, 04:57 -0700

    That sounds intriguing.

    photos of the dark limb can easily show nearby faint stars, and an automatic astrometric solution should then be possible. Since that imagery would be taken at some known UT, the result, from at least two stars in the image, is a position fix in latitude and longitude with no horizon and no sextant required.

    So if I rephrase that, you'd determine the RA/Dec of the centre of the Moon, as projected on the celestial sphere from the point of view of the observer, by comparing the outline of the Moon with the known RA/Dec coordinates of the surrounding stars. (I suppose the more stars the better, as the errors would average out more.) Then using the real 3D coordinates of the Moon at the given UT, you can draw a line from that RA/Dec on the celestial sphere in infinity passing through the (actual) centre of the Moon, and the intersection of this line with the surface of the Earth is the position of the observer. In other words, we measure the (two-dimensional) parallax of the Moon very precisely to get our position.

    A back-of-the-envelope calculation suggests that with 1000px across the Moon and other typical conditions, you can get about 1 pixel of parallax per 5 km on the surface of the Earth. Which is not very sensitive; I'd guess that greater uncertainties in parallax than that would come from uncertainties in refraction and the topography of the Moon, so measuring more precisely probably won't help? It should get a bit better with the Moon at high altitudes, at least.

    Is that what you have in mind?

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